1. Technical Field
The present invention relates to a fuel cell apparatus for vehicles, and particularly, to a fuel cell apparatus for vehicles including a fuel cell stack using air as a reaction gas and a coolant.
2. Relevant Art
There are vehicles having a set of fuel cell stacks mounted thereon as a power source, for instance, electric vehicles and hybrid vehicles. There are known structures for mounting fuel cell stacks, including a structure having fuel cell stacks disposed in a space between an under-cover and a floor panel under a rear passenger seat (refer to Japanese Patent Application Laying Open Publication JP 2010-234992 A), and a structure having fuel cell stacks disposed in an engine room (refer to Japanese Patent Application Laying Open Publication JP 2012-25294 A).
Fuel cell stacks are each made as a combination of a set of one or more unit stacks, and a stack casing constituting an outer cover of the unit stack set. Each unit stack is composed of multi-layered fuel cells, and a fuel cell enclosure integrally enclosing the fuel cells. The fuel cell enclosure has an air introducing aperture for introducing air to internal air supply channels (sometimes referred to as cathode-end channels), an air out-leading aperture for leading out unused air from air discharge channels communicating with the air supply channels, a fuel gas channel connecting part for supplying fuel gas being hydrogen gas to internal fuel gas channels (sometimes referred to as anode-end channels), and a purge gas channel connecting part for discharging a purged gas (referred herein to as a purge gas) containing hydrogen gas from purge gas channels communicating with the fuel gas channels.
For the fuel gas, gaseous hydrogen filled in a high-pressure hydrogen bomb is pressure-reduced to a desirable pressure at a pressure reducing valve, and supplied to the fuel gas line connecting part, by a quantity as needed. Air is taken from outside a vehicle, conditioned through a heat exchanger and a humidifier to a combination of temperature and humidity needed for high-efficient power generation, and supplied to the air introducing aperture. Fuel cells have their fuel electrodes and air electrodes, which are connected to associated apertures or channel connecting parts through individual networks of channels formed in the fuel cell enclosure.
At each fuel cell stack, the stack casing has ‘communication aperture areas’ (referred herein sometimes simply to as ‘aperture areas’) communicating with apertures formed in fuel cell enclosures of the one or more unit stacks, as necessary.
Power generating reactions in fuel cells produce by-product water at their fuel electrodes, spreading moisture vapor in channels conducting fuel gas. Some channels may have condensed vapor or dew or clustered water, undergoing an occasional blocking.
In this regard, fuel cell apparatuses have a purge function of purging fuel gas channels, flushing out water and vapor, for the prevention of blocking, and are adapted to make such a purge irrespective of the vehicular running condition. Such fuel cell apparatuses are adapted to make a purge even in a normal operation, as necessary for an adjustment of stack internal pressure or such. Upon a purge at a fuel cell stack, there are resultant purge gases lead out of purge gas channel connecting parts provided at fuel cell enclosures of unit stacks, and joined together to discharge from a purge gas line connecting part provided at a stack casing of the fuel cell stack to an associated purge gas line.
Such purge gases contain fuel gas (hydrogen gas), and are diluted to vent into atmosphere. In this regard, purge gases containing fuel gas (hydrogen gas) are inflammable, and have tendencies to inflame if the hydrogen concentration exceeds 4% by volume. Further, purge gases containing fuel gas (hydrogen gas) have tendencies to instantaneously inflame if the hydrogen concentration exceeds 18% by volume. Accordingly, purge gases containing fuel gas (hydrogen gas) to be vented to atmosphere should have hydrogen concentrations not exceeding 4% by volume.